1. Field of the Invention
The present invention pertains to a pipeline survey pig having a series of resilient cup support members which may be adjusted with respect to the pig body to selectively position the center of stiffness and a removable instrument chassis for the pig body for supporting an instrument cluster and power supply batteries.
2. Background
The adaptation of inertial type navigation instruments for use with pipeline survey pigs provides for accurate measurement of the curvature and displacement of pipelines due to subsidence and heaving of the earth on or in which the pipeline is supported. However, the packaging of the instrumentation, including the inertial reference unit and its power supply batteries, poses certain problems with regard to the physical arrangement of these components within the confines of a pig body structure and with regard to suitable heat transfer between the instrument components and the exterior of the pig body.
Another problem associated with a particularly unique pipeline survey pig concept using an inertial navigation unit pertains to providing for the center of stiffness of the pipeline pig and its support structure to be located coincident with or relatively close to the pig center of gravity. Although this is a desired feature, as described in co-pending U.S. Patent application Ser. No. 944,308 filed Dec. 18, 1986 and now U.S. Pat. No. 4,747,317 in the name of Pedro F. Lara and assigned to the assignee of the present invention, adjusting the location of the center of stiffness to a desired location in relation to the center of gravity, poses certain problems in the construction of the pig support structure.
The abovementioned problems associated with providing an improved pipeline survey pig have been addressed and overcome by the improved pig support structure and instrument chassis arrangement of the present invention.